Installation for the power assist of actuating devices in motor vehicles, especially in a hydraulic brake system

Abstract

An installation for the servo-assist of actuating devices in motor vehicles, especially of a hydraulic brake system, in which a control member, such as the brake pedal, acts on an actuating device, such as a master cylinder of a two-circuit brake system by way of a servo-member; a hydraulically actuatable servo-unit is thereby arranged between the control member and the actuating device whose first part is supported at the control member and whose second part is connected with the actuating device; the actuation of the servo-unit is controllable from a hydraulic pressure medium source in the manner of a follower control by means of a control device connected with the control member.

We claim: 
     
       1. An installation for the force assist of brake actuating means in an automobile comprising: actuating means,   an operating member for acting upon said actuating means,   a servo-unit having a housing displaceably guided upon support means for enabling said operating member to act upon said actuating means, and including amplifier means between the operating member and the actuator means, said amplifier means comprising a piston engageable by said operating member and positioned within a cylinder so as to divide said cylinder into plural chambers, said piston having one side exposing a first effective cross-sectioned area to a first of said chambers and a second oppositely directed side exposing a second smaller effective cross-sectional area to a second of said chambers, said servo-unit further comprising a first portion of the housing connected with the operating member, a second portion of the housing operatively connected to the actuating means, and control means for controlling the actuation of said servo-unit in the manner of a follower control providing a feedback to the operating member as to the applied pressure from a hydraulic pressure medium source by means of a first control device operatively connected with the operating member, and a second control device for enabling said operating member to act upon said actuating member upon failure of said hydraulic pressure medium source, said second control device including valve means communicating said one side of said piston with said hydraulic pressure medium source and said second side of said piston with a return in a first position of said valve means and discontinuing said communication in a second position of said valve means, said valve means being displaced from said first position to said second position upon failure of said hydraulic pressure medium source.   
     
     
       2. An installation according to claim 1, characterized in that the actuating means includes a master cylinder of a hydraulic brake system, and said operating member is a brake pedal. 
     
     
       3. An installation according to claim 2, characterized in that the master cylinder forms part of a two-circuit brake system. 
     
     
       4. An installation according to claim 3, characterized in that the pressure medium is fed to the servo-unit by way of said valve means which is held in its open position in dependence on the pressure in the hydraulic pressure medium source and which in case of pressure decrease or pressure failure is displaceable by spring force into its second position in which it connects with each other the two sides of the piston of the servo-unit. 
     
     
       5. An installation according to claim 4, wherein the pressure medium is conducted to the servo-unit by way of a shifting valve means which is electromagnetically held in a position opening up the flow from the second control device through the shifting valve means and which in case of current failure is displaceable by a spring force into a position opening up the flow from the first control device through the shifting valve means. 
     
     
       6. An installation according to claim 5, characterized in that the solenoid of the shifting valve means is provided with an energizing circuit and a switch which is arranged in the energizing circuit of the solenoid of the shifting valve means opens upon contacting the operating member. 
     
     
       7. An installation according to claim 3, characterized in that the pressure medium is conducted to the servo-unit by way of a shifting valve means which is electromagnetically held in a position opening up the flow from the second control device and which in case of current failure is displaceable by a spring force into a position opening up the flow from the first control device. 
     
     
       8. An installation according to claim 7, characterized in that the solenoid of the shifting valve means is provided with an energizing circuit and a switch which is arranged in the energizing circuit of the solenoid of the shifting valve means opens upon contacting the operating member. 
     
     
       9. An installation according to claim 1, characterized in that the pressure medium is fed to the servo-unit by way of a closure means which is held in its open position in dependence on the pressure in the hydraulic pressure medium source and which in case of pressure decrease or pressure failure is displaceable by spring force into its closing position in which it connects with each other the two sides of the piston of the servo-unit. 
     
     
       10. An installation according to claim 1, wherein said valve means blocks flow of the hydraulic pressure medium into or out of said chambers when said valve means is in its second position. 
     
     
       11. An installation according to claim 1, characterized in that said servo-unit includes a housing rigidly connected with a piston in a master brake cylinder, and said piston of the servo-unit is connected to the operating member with a relatively short lever arm. 
     
     
       12. An installation according to claim 11, characterized in that the pressure medium is fed to the servo-unit by way of a closure means which is held in its open position in dependence on the pressure in the hydraulic pressure medium source and which in case of pressure decrease or pressure failure is displaceable by spring force into its closing position in which it connects with each other the two sides of the piston of the servo-unit. 
     
     
       13. An installation according to claim 12, characterized in that the first control device as well as the valve means are arranged in the housing of the servo-unit and both are constructed in the manner of a hydraulic piston slide member, the piston slide member of the control device engaging at the operating member with a relatively large lever arm by way of a control linkage. 
     
     
       14. An installation according to claim 11, characterized in that said control device comprises a piston slide member acted upon by said operating member with a relatively large lever arm in comparison to that of said servo-unit piston, in that axially only a slight path is present for the piston slide member of the control device within the housing of the servo-unit and in that after overcoming this path, the piston slide member abuts in the housing for purposes of a mechanical force transmission.